As of April 2007:
-16 nights on Keck-II/DEIMOS
-13876 stars in the outer regions of M31 and its satellites
with radial velocities and Calcium II Triplet [Fe/H]
measurements.
-6 new dwarf satellites (AndIX,XI,XII,XIII,XV,XVI)

The dwarf spheroidal galaxy AndXII:
First evidence for late infall.

Further theoretical context
for AndXII from Sales, Navarro, Abadi, Steinmetz (astro-ph/0704.1773)
"High-velocity satellites approaching M31 in projection are
unlikely to be escapers, but rather satellites on their first approach.
This interpretation is probably the most appropriate for And XII
[unique for the satellites of M31].
As discussed by Chapman et al. (2007), And XII
is almost certainly farther than M31 but is approaching us at much
higher speed (281 km/s faster) than M31. This implies that And XII
is actually getting closer in projection to M31
making the interpretation
of this satellite as an escaping system rather unlikely."
The figure below (from our paper ``Strangers in the night'') highlights AndXII as the one known
M31 satellite which is at the
limit of escaping from M31's gravitational grasp, for typical mass models
of M31.
Further theoretical context, movies and simulations from Ludlow et al. (2007)
From the simulations of Ludlow et al. (2007), who
have looked explicitly at high velocity structures
falling into halos of similar total mass to the Local Group at late times.
The
distribution of dark matter particles at z=0 within 2 Mpc/h of the galaxy
(black points -- 200^3 particle simulation) contrasted with
red points marking the location of gravitationally bound
substructures. It is clear that the filaments contain most of the
matter and subhalos in the nearby volume, and they intersect at the
location of the galaxy.
The cosmology is flat LambdaCDM:
Omega_M = 0.25,
Omega_Lambda = 0.75,
H_0 = 0.73.
The simulation shows
M_{200} = 48.4 (10^10 M_sun/h)
R_{200} = 127.6 (kpc/h)
C_{200} = 10.6
V_{max} = 148.2 (km/s).
The simulation was undertaken with Gadget2 (Springel V., et al., 2005, MRNAS, 364, 1105).